1. Field of the Invention
The invention is a process for coproducing perchloroethylene, phosgene, and silicon tetrachloride by contacting carbon tetrachloride with porous silica at a temperature from 800.degree. to 950.degree. C.
2. Prior Art
Perchloroethylene (C.sub.2 Cl.sub.4 ; tetrachloroethylene), phosgene (COCl.sub.2 ; carbonic dichloride), and silicon tetrachloride (SiCl.sub.4 ; tetrachlorosilane) are all widely used in industry. Processes for making them individually are well known but the coproduction of all three seems not to have been carried out heretofore.
Perchloroethylene is usually made by the pyrolysis of carbon tetrachloride (CCl.sub.4 ; tetrachloromethane) at a temperature of 600.degree. to 1500.degree. C. In commercial practice, the pyrolysis is conducted in a furnace by contacting carbon tetrachloride vapor with a heated porous bed of carbon or silicon carbide shapes (U.S. Pat. No. 1,930,350).
Phosgene is commonly produced by the reaction of carbon monoxide and chlorine.
Silicon tetrachloride may be made by the reaction of silica in a heated porous bed with chlorine and carbon (coke) or with phosgene (Halogen Chemistry, vol. 2, p. 177-179 (1967), V. Gutmann ed., Academic Press, London/New York). However, it has been reported that little or no silicon tetrachloride is produced when carbon tetrachloride is passed over silica or silicic acid, even at a red heat (L. Meyer, Ber. 20, 681-683 (1887)).
Perchloroethylene and phosgene have been coproduced from carbon tetrachloride, but carbon monoxide is an essential reactant, the temperature is 150.degree. to 300.degree. C., and an unusual catalyst is required (U.S. Pat. No. 3,364,272).
Perchloroethylene and chlorosilanes have been coproduced from carbon tetrachloride, but only by reacting the latter with elemental silicon in the presence of a metallic catalyst. Temperatures above 300.degree. C. must be avoided to minimize carbonization (U.S. Pat. No. 2,381,001).
Phosgene has apparently never been coproduced with silicon tetrachloride. Rather, in contact with silica at 1000.degree. C., phosgene is consumed, being converted to silicon tetrachloride (Budnikoff, Z. angew. Ch. 39, 765 (1926)).